Anechoic chambers are typically used in conjunction with the generation of electromagnetic radiation in the radio frequency (RF) range for applications such as radar. When RF radiation is generated in the anechoic chamber, it is desirable to prevent the RF radiation from escaping in an uncontrolled manner from the chamber. It is desirable to prevent the RF radiation from escaping, for instance, because the radiation could pose a health risk to personnel working in the vicinity of the chamber. Additionally, there may exist circumstances when it is desirable for the location or the existence of the chamber having RF radiation not to be revealed. Uncontrolled escape of RF radiation from the chamber could be detected by entities who are not to know of the chamber's existence and alert them to the presence of the chamber.
The uncontrolled escape of RF radiation from the chamber could occur through various cracks and openings in the chamber. For electromagnetic radiation below essentially 10 GHZ, there is known devices, such as RF connectors, which prevent the escape of the RF radiation. Moreover, as the radiation decreases in frequency (thus the wavelength increases in length), the radiation requires a larger opening to fit through in order to escape from the chamber. By proper construction techniques, many of the concerns over low frequency radiation loss can be eliminated.
However, as the need for higher frequency RF radiation (greater than 10 GHZ) arises in order to increase the radar's resolution, it becomes more and more difficult to effectively prevent the high frequency RF radiation from escaping through necessary openings, such as electrical feed channels that penetrate the chamber. The electromagnetic RF energy under such circumstances can literally propagate along the cables extending through the channel in order to escape the confines of the chamber. Heretofore, techniques available to control the loss of radiation do not address this problem. For instance, U.S. Pat. No. 4,590,710 discloses a seal assembly for an enclosure, which attenuates or eliminates frequencies through the enclosure. The seal assembly is used for a door such that when the door is shut, there is no frequency leakage through the door. In another example, U.S. Pat. No. 3,894,169 discloses damping means capable of being applied as paint to absorb sound waves impinging thereon.
The present invention provides for the attenuation or elimination of escaping electromagnetic radiation through openings or apertures which cables extend.